A conventional shoe sole (40) is shown in FIG. 5 and comprises an inside part (30) connected to the under side of the sole (40) which is made of soft material with a first density and the inside part (30) is made of hard material with a second density. The inside part (30) is used to maintain the shape of the sole (40) and provides suitable support to the foot. The process to connect the inside part (30) to the sole (40) consists of defining a recess (41) in the under side of the sole (40) and then gluing the inside part (30) in the recess (41). Because the densities of the sole (40) and the inside part (30) are different, the manufacturers have to prepare the sole (40) and the inside part (30) separately, and the periphery defining the recess (41) is required to precisely match the inside part (30) so as to firmly connect the inside part (30) to the sole (40). Furthermore, when the inside part (30) is received in the recess (41), a process is further taken to make sure that the inside part (30) does not shift. The glue has an inherent shortcoming in that the glue hardens after a period of time and forms an obvious, inflexible boundary between the sole (40) and the inside part (30). Notwithstanding that a sole (40) with two different colors is welcomed by consumers in the market, a visible boundary formed by the glue between the sole (40) and the inside part (30) will destroy the aesthetic value of the shoe.
The present invention intends to provide a method for manufacturing shoe sole with integral parts of different densities. The method is easily achieved and makes the inside part firmly be connected to the sole member.